Many hydrocarbon wells are produced by electrical submersible well pump assemblies (ESP). A typical ESP includes a centrifugal pump having a large number of stages, each stage having an impeller and a diffuser. An electrical motor couples to the pump for rotating the impellers.
A pressure equalizer or seal section connects to the motor to reduce a pressure differential between lubricant in the motor and the hydrostatic pressure of the well fluid. The pressure equalizer has a motor lubricant passage leading from a flexible barrier, such as a bag or bellows, into the interior of the motor. The motor lubricant passage is always open to communicate well fluid pressure applied in the pressure equalizer to the flexible barrier to the motor lubricant in the motor. Normally, a well fluid passage leads into the pressure equalizer to a side of the flexible barrier opposite the side in contact with lubricant.
With most prior art ESP's, the pressure equalizer or seal section is located between the motor and the pump. In others, the pressure equalizer is mounted below the motor. Whether above or below, the movement of the flexible barrier occurs only in direct response to forces exerted by the well fluid and lubricant on the flexible barrier.